The invention relates to a sensor for noncontacting thickness gauging on films, in particular blown films, with a sensor head and a mount for the sensor head, the sensor head comprising at least one noncontacting sensor element for gauging the thickness in accordance with the physical properties of the film.
Large varieties of sensors for noncontacting thickness gauging are known from practice. For example, the thickness of film tapes is monitored during production with two oppositely arranged displacement measuring sensors with the film tape advancing between the displacement measuring sensors. In practice, this sensor arrangement is problematic, since displacement measuring sensors normally display a nonlinear behavior. Fluttering of the film tape being monitored, different tape thicknesses, or the movement of the tapes toward or away from the displacement measuring sensors will cause measuring errors that are due to the nonlinear behavior of the displacement measuring sensors in the measuring range.
For thickness measurements on blown films the known sensor arrangement is totally unsuited, since a blown film cannot be guided between the two displacement measuring sensors. For this reason, it has until now been common practice to use sensing sensor arrangements for gauging the thickness of blown films. However, since thickness gauging should not occur during a stage of the production process, when the film material is still soft and deformable, a sensing thickness measurement will always leave sliding marks of the sensor head, unless it even leads to damage to the film tape and to tearing of same in the extreme case.
It is therefore the object of the invention to provide a sensor for gauging the thickness on films, which makes it possible to perform on the one hand a noncontacting thickness measurement, in particular also on blown films, and which largely prevents on the other hand measuring errors that are caused by the movement of film during the production process.